Beamsplitters/combiners are currently used in many applications such as broadband data communications. FIG. 1 illustrates a prior art system that uses multiple single channel beam combiners. Each single channel combiner includes two inputs, an output, and various micro-optic components such as a spatial walk-off polarizing crystal and collimators. The input collimator operates to focus light beams A and B received from the input fibers onto the spatial walk-off polarizing crystal.
A spatial walk-off polarizing crystal is a crystal of birefringent material that splits an unpolarized light beam into two orthogonally polarized light beams. When an anisotropic (birefringent) crystal is cut at a certain angle relative to its optical axis, the crystal will cause a component of light in a particular polarization direction to be diverted into a different path as it passes through the crystal. The amount of divergence is proportional to the thickness of the crystal. The direction that the polarization component is diverted is referred to as the walk-off direction of the crystal. A birefringent crystal, however, will only divert the polarization component in a polarization plane parallel to the walk-off direction and will not effect the polarization component in a plane perpendicular to the walk-off direction. In addition, a walk-off crystal is a reciprocal device such that the deviation angle of light passed through the crystal in a forward direction is opposite that of light passed through the crystal in a backward direction. In this manner, two orthogonally polarized light beams A and B are combined into a single light beam when passed through the spatial walk-off polarizing crystal in the direction from the input to the output fiber. The single beam is propagated to an output collimator that focuses the single beam into the output fiber.
Such single channel beam combiners typically have a cylindrical shape that may be 65 mm in length and 5 mm in diameter. The spatial walk-off polarizing crystals used in these beam combiners may each run on the order of a few hundred dollars and may only be available from only a limited number of vendors. As such, one problem with such micro-optic combiners is their increased manufacturing cost. The increased manufacturing cost is due not only to the multiple individual assemblies that are required for each channel, but also the high cost of the crystals (e.g., spatial walk-off polarizing crystal) used in these combiners. When many of these crystals are required for construction of multiple micro-optic combiners, the increasing cost greatly detracts from the desirability of these devices. In addition, their limited availability may also make these micro-optic combiners undesirable due to possible supply shortages.
Another problem with such micro-optic devices is that they have very large dimensions, making them undesirable for use in systems that require small device geometries.